how can i use my iphone4s to another carier?
You will need to contact Verizon to get the SIM slot unlocked. Note that this works only for international use; Verizon will not unlock the iPhone to use with any other US cell carrier.
It can not be used on any other US carrier. Ever. If you are a Verizon customer in good standing, you can get the SIM slot unlocked for international travel. If not, you're out of luck. You can't use it on anthing other than Verizon.
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